1. Field of the Invention
The present invention relates to a lost foam pattern for molding and a method of making same, and in particular to an improvement of a lost foam pattern for molding in which foam is decomposed and gasified by molten metal and then replaced with molten metal in a lost foam pattern molding process and a method of making the same.
2. Description of Related Art
A conventional lost foam pattern for molding employs two kinds of synthetic resin, namely, expanded polystyrene and expanded polymethylmethacrylate resin. When the lost foam pattern is made out of expanded polystyrene, a carbonizing phenomenon in castings occurs because a large quantity of carbon is produced during the molten metal pouring process. On the other hand, when the lost foam pattern is made out of the expanded polymethylmethacrylate resin, the molten metal flows in the reverse direction during the molten metal pouring process, because the expanded polymethylmethacrylate resin is gasified at a high speed during a decomposing process and a large quantity of gas is produced.
Japanese Utility Model Laid-Open Publication No. 3-85146 discloses a lost foam pattern for molding in which a hollow lost connecting pipe is provided between the bottom portion of a sprue and a runner, and a product foam pattern is connected with the hollow lost connecting pipe through a solid runner foam pattern and the gate portion foam pattern.
According to the conventional lost foam pattern for molding disclosed in the Japanese Utility Model, when the lost foam pattern is made out of the expanded polymethylmethacrylate resin, the lost connecting pipe can prevent the molten metal from flowing in the reverse direction during the molten metal pouring process. However, on the other hand, the conventional lost foam pattern has some disadvantages because it has a low strength for supporting the product form and produces misruns and the like.